The utility of using DNA adducts as biomarkers for dietary heterocyclic amine (HA) exposure and individual susceptibility in humans remains to be determined. Significant effort has been devoted to the demonstration of HA bioactivation and DNA adduct formation using animal models, but little effort has been devoted to proving the utility of adducts in humans. It is our hypothesis that adducts will remain of limited use until high-throughput, quantitative and sensitive analytical methods are available and the variability in adduct levels for a given exposure, and the factors that affect individual variation, are better understood. It is our belief that to evaluate the use of adducts as biomarkers of exposure and risk for HAs in humans, extremely sensitive analytical methods that do not require the administration of radioisotopes must be developed. The purpose of this proposal is to expand our understanding of the use of adducts as biomarkers through the development of sensitive analytical methods, as well as determination of the adduct variation, and the factors that influence it, using a combination of animal models and human studies. Unique to this proposal is the use of accelerator mass spectrometry (AMS), which allows us to quantify isotope-labeled adducts and metabolites with a sensitivity and precision not routinely available with other methods. Specifically, we will (1) Complete the characterization of adducts formed by PhIP and MeIQx in DNA, and develop methods for the synthesis and handling of these adducts for use as standards; (2) Develop and validate an AMS-based isotope postlabeling assay using the characterized HA adducts so that adducts can be assessed in populations of people without the need for administration of isotope-labeled HAs, yet utilize the sensitivity and precision of AMS, and (3) Determine the variability of DNA adducts in selected human and animal populations and whether age, sex, and geno(pheno)type influence adduct levels following a well-defined exposure dose. The results of this project should result in new quantitative and sensitive analytical methods for measuring adducts in humans. Importantly, it will lead to a more complete understanding of the nature of HA adducts and whether they hold promise as biomarkers for exposure, and susceptibility on an individual basis.